It is common for a foal to be born with one of several defects in its legs. For example, a foal may have a deviation, which is a misalignment of the leg, particularly, the knee joint. If the knee joint is curved outwardly, the deviation is termed a "varus deviation", whereas if the leg is curved inwardly, it is a "valgus deviation." A varus deviation of the knee joint is often accompanied by a valgus deviation of the ankle joint, and vice versa.
It is often that a foal is born with a leg which cannot be extended, and this is termed a "contracture." Other defects or injuries are also common.
These defects become particularly significant when the animal is expensive, such as the offspring of a racehorse. Accordingly, several techniques have been developed in the prior art for correction of these defects.
Perhaps the most popular technique in use is to place the deformed leg in a plaster cast to allow it to grow in the proper manner. This technique is difficult to use and has poor results because the horse considers the plaster cast to be an extremely uncomfortable foreign object and often injures itself trying to escape from the cast.
Other devices are known in the art which are used for various purposes, other than the correction of the specific defects mentioned above. U.S. Pat. No. 3,439,670 (Schuerch) teaches a support for use on a weak or injured leg of a horse. This includes three sections which are attached to the hoof and leg of a horse to provide support. The device fits tightly onto the leg of a horse, and the only restriction to movement of the joints arises from a spring or rod which may be attached between adjacent sections.
U.S. Pat. No. 901,592 (Clegg) teaches a device for preventing the front legs of a horse from hitting each other. This device includes a single joint attached to a horse's foreleg for restricting the movement of the leg.
In addition to devices designed for a horse's leg, it is known to attach braces of various sorts to a human leg. For example, U.S. Pats. Nos. 4,361,142; 4,370,977; and 4,433,679 (Lewis et al., Mauldin et al., and Mauldin et al.) show such braces. These are rarely of any use in treating defects in the leg of an animal such as a horse because of the marked anatomical differences between a leg of a human and a leg of another animal.